This invention relates to a control circuit for driving a direct current (D.C.) motor and, in particular, to a control circuit for applying a reverse current through a motor to control induced currents.
In the prior art, D.C. motors rather than A.C. motors are used for many applications because of their greater efficiency, compact size, and the ease with which the direction of rotation can be reversed. A problem develops when one does not wish to run the motor continuously or at a steady speed. The question is simply how to control the current through the motor.
A variety of techniques have been proposed or used in the prior art for controlling a D.C. motor. A common technique is to control power by using a variable duty cycle drive current. This technique is also known as pulse width modulation (PWM). A difficulty with this technique, and others, is the need to dissipate reverse current through the windings when the pulse is terminated. Another difficulty is the inertia of the rotor, combined with the reverse current, upsetting the position of the rotor when precise movement is desired. A further difficulty is the fact that PWM systems generally run at a particular frequency, which may restrict the rate at which the motor can be stepped or cause problems with resonance in the system due to insufficient resolution of the resultant current waveform.
In view of the foregoing, it is therefore an object of the present invention to provide an improved current regulator for D.C. motor control.
Another object of the present invention is to provide an improved control system using pulses.
A further object of the present invention is to provide a free-running, pulse control of D.C. motors operating over a wide range of loads.